Various pressure relief devices for inflatable tires have been proposed in the prior art. U.S. Pat. No. 3,830,249 discloses a device in which a pressure relief ball is maintained in a seated position by a force applied by a compression spring until the air pressure within the tire exceeds a set pressure. When the set pressure has been exceeded, the pressure relief ball is unseated from the body, and surplus air escapes from the tire via the pressure relief device.
U.S. Pat. No. 4,660,590 is concerned with an inflation pressure regulator. A sealing section of a flexure member is urged into sealing contact with a seat. When the tire has been inflated to the pressure rating of the regulator, the pressure in a first chamber will exert sufficient force to cause flexing in a portion thereof and a consequential movement of the sealing section away from the seat surface, allowing air to escape via an exhaust aperture.
WO 2007/134611 discloses a pressure relief device for an inflatable tire comprising a body having a pressure relief mechanism and a conduit being provided as a passage in a pin for releasing a stem of a tire.
U.S. Pat. No. 5,365,967 discloses a tire pressure indicator which includes a valve stem over-pressure indicator and a valve stem cap under-pressure indicator. When the over-pressure condition is reached within a tire, air flows through lateral ports of the valve stem to escape around a regulator O-ring into a chamber, and air from the chamber escapes through ports adjacent reeds to make a whistling sound so long as over-pressure conditions endures.
Pressure relief devices capable of providing audible signals in response to the filling or adjustment of the pressure in the tire exist. One generally recognised problem with such audible signals is that they cause frustration for the user and for others when the filling process becomes noisy.